1. Field of the Invention
The present invention is in the field of manufacture of copper intermediate stock intended to be subsequently processed by known methods for formation into wire, sheet, tubes, strip, buss bars and the like.
2. The Prior Art
A significant proportion of the cost of manufacturing finished products of copper, such as wire, sheet, rod, etc., is attributable to the fabrication of the intermediate forms of the material from which the final products are to be manufactured.
A procedure which has successfully been adopted to reduce the cost of producing intermediate stock is the so-called accretion method wherein a continuous length of seed rod or wire of purified copper is progressively advanced under controlled conditions through a crucible containing molten copper, with the result that increments of the molten copper accrete on the advancing rod or wire. The resultant substantially thicker rod or wire is comprised of a solid body of substantially homogeneous copper suitable for subsequent processing.
Various procedures for refining of copper by accretion are disclosed in the patent art, such as, by way of example, in U.S. Pat. Nos. 3,008,201, 3,060,053 and 3,235,960.
A requirement of the accretion process as illustrated in said patents is that the molten copper in the crucible through which the seed rod is drawn be exceedingly pure, and especially be free of oxygen contaminants, either in the free state or combined with the copper as oxides. Specifically, it is stated in U.S. Pat. No. 3,060,503 that the oxygen content of the melt in the accreting crucible not exceed about 20 parts per million (ppm).
Heretofore the production of a melt of a requisite purity and freedom from oxygen contamination has required the use of an electrical melting furnace. All other means for melting the copper, and specifically fuel fired furnaces, in which combustion takes place in contact with the copper being melted, have resulted in the incorporation in the melt of an unacceptably high oxygen content.
Increasing charges for electrical energy, particularly in certain areas of the United States, have so greatly increased the costs of electrical melting furnace procedures as to make their use prohibitively expensive.
Attempts have been made to utilize fuel fired melting furnaces to provide molten copper to the accreting crucible. However, even the most efficient of such fuel fired furnaces, in the sense that the same produces copper with a low oxygen content, namely a furnace such as described in U.S. Pat. No. 3,199,977, results in a copper melt containing approximately 100 ppm oxygen.